Which music professionals might work under contract with a musical teaching group or a music store? background vocalistsprivate instructorstheatre musiciansperforming artists

The correct option is PRIVATE INSTRUCTORS.
Private music instructors can work with musical teaching group or a music store in order to provide instrumental, vocal  and music training to people of all ages. Music private instructors normally work at different levels teaching either individuals or groups. 

For example you could start a retail clothing store because you would need to have skills in business and you could start an photography business you would need to have skills in photography. hope this